1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a turbine blade of spar and shell construction with cooling of the shell and the platform.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine includes a compressor to compress air, a combustor to burn the compressed air with a fuel and produce a high temperature gas flow, and a turbine to convert the energy from the high temperature gas flow into mechanical energy used to drive the compressor and, in the case of an aero engine to drive a bypass fan, or in the case of an industrial gas turbine (IGT) engine to drive an electric generator.
The efficiency of the engine can be increased by passing a higher temperature gas flow into the turbine. However, the inlet temperature of the turbine is limited to the material properties of the first stage blades and vanes. Higher inlet turbine temperatures can be obtained by a combination of material properties (allowing for higher melting temperatures) and improved airfoil cooling. Since the compressed air used for airfoil cooling is bled off from the compressor, maximizing the amount of cooling while minimizing the amount of cooling air used is a major objective for the engine designer.
To allow for higher temperatures, turbine airfoils can be made from a spar and shell construction. U.S. Pat. No. 7,080,971 B2 issued to Wilson et al on Jul. 25, 2006 and entitled COOLED TURBINE SPAR AND SHELL BLADE CONSTRUCTION discloses a prior art turbine blade with a spar and shell, the entire disclosure incorporated herein by reference. The shell is made from a very high temperature resistant material and with thin walls in order to allow for high heat transfer coefficient from the outside surface to the inside for best cooling. The spar functions as a support for the shell and a channel forming member for cooling air.